Regio‐ and Chemoselective Reduction of Nitroarenes and Carbonyl Compounds over Recyclable Magnetic FerriteNickel Nanoparticles (Fe3O4Ni) by Using Glycerol as a Hydrogen Source

Functionalized magnetic nanoparticles (MNPs) have emerged as viable alternatives to conventional materials, not just for heterogeneous, but also for homogenous catalysis because they offer an added advantage of being magnetically separable, thereby eliminating the requirement of catalyst filtration. A variety of catalytic systems involving metal-supported MNPs have been devised and used in synthetic organic reactions. For example, immobilized palladium complexes with N-heterocyclic carbene ligands (NHC-Pd complexes) on the surface of ferrite-MNPs were used for palladium cross-coupling reactions. A more demanding protocol for the preparation of palladium nanoparticles supported on phosphate-functionalized MNPs was reported by Yinghuai and co-workers with success on Suzukiand Heck coupling reactions. Xia et al., used a magnetically separable Pd/Fe3O4 catalyst for a carbonylative Sonogashira coupling reaction. Free nano-g-Fe2O3 have been shown to be active, stable, and highly selective catalysts for various oxidations with high turnover number (TON) and excellent selectivity. Reduction of organic substrates such as nitro, azido, and carbonyl compounds is of the utmost importance in organic synthesis. This is a fundamental process with a variety of applications in pharmaceutical industries and in the synthesis of biologically significant compounds. There have been a number of reports on hydrogenation reactions using noble metal catalysts, however these catalysts present as a major drawback its high cost. Recently remarkable economic non-toxic and effective iron nanoparticles catalysts were reported for specific reduction. Recently, glycerol has gained increasing attention as an alternative sustainable solvent for catalytic and non-catalytic organic transformations because of its unique combination of physical and chemical properties, such as polarity, low toxicity, high boiling point, and biodegradability. Very recently, glycerol has also been used in transfer hydrogenation reactions. The reduction of nitro as well as carbonyl compounds with hydrogen-transfer reagents is a much safer and more benign process than reactions involving molecular hydrogen, metal hydrides, or soluble metals. Varma and Manorama already addressed this issue by using palladium or nickel on dopamine-terminated surface of Fe3O4 for hydrogenation reactions. 13] The complexes of the secondor third-row transition metals, such as Rh, Ru, Ir, and Pt are among the most efficient catalysts devised. Much less attention has been devoted to the hydrogen-transfer reduction of carbonyl compounds using inexpensive metals. In continuation of our efforts to develop protocols for green raw materials and heterogeneous catalysis for hydrogen-transfer reactions and nano-catalysis, we propose to use glycerol as hydrogen donor as well as solvent in the reduction of nitro and carbonyl compounds using a new, efficient, recyclable, and inexpensive ferrite-nickel magnetic-nanoparticles (Fe3O4-Ni MNPs). This protocol avoids multistep processes and linkers between the metal and ferrites rendering the present protocol cost-effective. Fe3O4-Ni MNPs were prepared by the simple wet impregnation method followed by chemical reduction (Scheme 1) and characterized by X-ray diffraction (XRD), inductive coupled plasma-atomic emission spectroscopy [a] Dr. M. B. Gawande, Prof. Dr. P. S. Branco REQUIMTE, Departamento de Qu mica Faculdade de CiÞncias e Tecnologia Universidade Nova de Lisboa, 2829-516 Caparica (Portugal) Fax: (+351)21-2948550 E-mail : m.gawande@fct.unl.pt mbgawande@yahoo.co.in p420@fct.unl.pt [b] Dr. A. K. Rathi Jubilant Chemsys Ltd., B-34, Sector-58 Noida-201301, New Delhi (India) [c] Dr. I. D. Nogueira Instituto de CiÞncia e Engenharia de Materiais e Superf cies IST, Lisbon (Portugal) [d] Prof. Dr. A. Velhinho CENIMAT/I3N Departamento de CiÞncias dos Materiais Faculdade de CiÞncias e Tecnologia Universidade Nova de Lisboa, 2829-516 Caparica (Portugal) [e] Dr. J. J. Shrikhande, Dr. U. U. Indulkar, Prof. Dr. R. V. Jayaram Department of Chemistry, ICT, Matunga, Mumbai (India) [f] Dr. C. A. A. Ghumman, Dr. N. Bundaleski, Prof. O. M. N. D. Teodoro Centre for Physics and Technological Research (CeFITec) FCT, UNL, Lisboa (Portugal) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201202380.